When compared to competitive VVA devices, the main advantages of the present HELP system are its simplicity and compact height. The VVA device disclosed in US Patent Application Publication No. 2003/0132813 A1 and U.S. Pat. No. 7,246,578 B2 are kinematically complex, adding four to six oscillating members per cylinder to conventional, direct acting and roller finger follower valvetrains, respectively. The greater the number of oscillating parts, the less stiff the system is dynamically and the less likely it is to obtain satisfactory high speed operation. This can be seen in these VVA devices' undesirable phase change characteristic in full lift as a function of engine speed.
Although the VVA device disclosed in U.S. Pat. No. 6,823,826 B1 offers an attractive packaging height, it is very complex as well. Moreover, with its internally and externally splined parts, it is a costly and noisy solution for varying valve lift.
In the present HELP system, only two oscillating members have been added to a standard, roller finger follower type valvetrain system to effect variations in lift, timing, and duration. By comparison, while the VVA device disclosed in U.S. Pat. No. 7,225,773 B2 also is kinematically simple with only two added parts per cylinder, the system adds considerable height to an engine.
Having fewer moving parts also simplifies the design tradeoffs associated with these mechanical devices. In the VVA device disclosed in U.S. Pat. No. 5,937,809, an input rocker is connected through a link to two output cams that also ride on the input camshaft. Because the mechanism comprises four moving parts per cylinder, it is difficult to provide a return spring stiff enough for high-speed engine operation that will still fit within the available packaging space. Since the present HELP system has only two moving parts, the total mass moment of inertia is much lower, and hence spring design is less challenging. In addition, because there are fewer parts, there are fewer degrees of freedom in the mechanism, which simplifies the task of design optimization to meet performance criteria by substantially reducing the number of equations required to describe the mechanism's motion.
As the cost of petroleum continues to fluctuate from increased global demands and limited supplies, the fuel economy benefits of internal combustion engines will become a central issue in their design, manufacture, and use at the consumer level. Production applications that apply a continuously variable valvetrain system to just the intake side of a gasoline engine can yield notable fuel economy benefits on FTP (Federal Test Procedure—USA) or NEDC (New European Driving Cycle) driving schedules, based on simulations and real vehicle testing. VVA when combined with Direct Injection (DI) in a gasoline engine can deliver even higher fuel efficiencies that are on par with diesel engines. The VVA/DI engine can become strategically important to America and other countries dependent on a gasoline-based transportation economy.
Likewise, the use of a continuously variable valvetrain for the intake side of a gasoline engine coupled with an Early Intake Valve Closing (EIVC) load control strategy can significantly lower engine-out NOx emissions by lowering an engine's effective compression ratio at light and moderate engine loads.
What is needed in the art is a simplified, inexpensive, and reliable system for varying the lift, duration, and timing of engine valves which employs relatively few moving parts and affords a relatively small packaging envelope in the engine compartment of a vehicle.
It is a principal object of the present invention to reduce the complexity, cost of manufacture, and difficulty of manufacture of a system for varying the lift, duration, and timing of engine valves.
It is a further object of the present invention to reduce the packaging envelope required for such a system relative to prior art systems.